The present embodiments relate to a contour collimator or an adaptive filter and to an associated method for adjusting a contour in a ray path in x-ray radiation.
A contour collimator is used in radiation therapy for the treatment of tumors. In radiation therapy, a tumor is irradiated with energy-rich radiation (e.g., with high-energy x-ray radiation of a linear accelerator). In such treatment, the contour collimator is brought into the ray path of the x-ray radiation. The contour collimator has an opening, through which radiation may pass. The contour of the opening is intended to correspond to the contour of the tumor. The contour thus forms an aperture for the passage of the x-ray radiation. This provides that the tumor, and not the adjoining healthy body tissue, is irradiated with the x-ray radiation. By embodying the contour collimator in a suitable manner, almost any given contour of a tumor may be mapped.
Collimators widely used for radiation therapy are multi-leaf collimators, as described, for example, in patent DE 10 2006 039793 B3. The multi-leaf collimator has a number of leaves (e.g., 160 leaves) able to be moved by motors in relation to one another to form the opening. The leaves include a material absorbing the x-ray radiation. Two packages of leaves are disposed opposite one another so that the leaves may be moved with end face sides towards one another or away from one another.
Each of the leaves is able to be displaced individually by an electric motor. Since there may be slight deviations in the positioning of the leaves between a required specification and the actual position of the leaves currently set, each leaf has a position measurement device, with which the position currently set may be determined.
In examinations with the aid of x-rays, it often occurs that the patient or organs of the patient exhibit a greatly differing absorption behavior with respect to the applied x-ray radiation in the area under examination. For example, in images of the thorax, the attenuation in the area in front of the lungs is very large, as a result of the organs disposed there, while in the area of the lungs, the attenuation is small. Both to obtain an informative image and also to protect the patient, the applied dose may be adjusted as a function of the area so that more x-ray radiation than necessary is not supplied. This provides that a larger dose is to be applied in the areas with high attenuation than in the areas with low attenuation. In addition, there are applications in which only a part of the area under examination is to be imaged with high diagnostic quality (e.g., with little noise). The surrounding parts are of importance for orientation but not for the actual diagnosis. These surrounding areas may thus be mapped with a lower dose in order to reduce the overall applied dose.
Filters are used to attenuate the x-ray radiation. Such a filter is known, for example, from DE 44 22 780 A1. This has a housing with a controllable electrode matrix, by which an electrical field that acts on a fluid connected to the electrode matrix, in which x-ray radiation-absorbing ions are present, is able to be generated. The x-ray radiation-absorbing ions are freely movable and move around according to the field applied. In this way, by forming an appropriate field, many or few irons may be correspondingly accumulated in the area of one or more electrodes in order to change the absorption behavior of the filter locally.